This invention relates to the heat treatment of steel articles, and in particular relates to induction heating, quenching, and tempering of steel sheets.
In order to improve the mechanical properties of metal articles, metal is typically subjected to time consuming, and therefore costly, heat treatment processes. To increase the hardness of a steel, a steel article may be subjected to a heating cycle at or above a temperature of the metal's critical temperature, followed by quenching the metal article. This process typically results in creation of a martensitic microstructure in steels. Martensitic microstructures, while relatively hard, are also known to be relatively brittle, and with less ductility. To increase the ductility of martensitic microstructures, such steels are often tempered, or heated to a temperature below the steel's critical temperature, whereby stresses built up in the steel during quenching are reduced. Such heating, quenching, and tempering processes are typically long to conduct, and accordingly, expensive.
In processing steel generally, and, more specifically, in forming anti-ballistic armor, it has until now been difficult to achieve a metal product having a combination of strength and ductility which could be manufactured without high cost, including extensive heat treatment time. For example, such a metal article should be able to resist penetration by armor piercing ammunition as well as fragments from improvised explosive devices, including explosively formed projectiles. We have found a method and apparatus for heat treating, quenching, and tempering a steel article whereby the article has desirable mechanical and microstructure properties, including properties which may be useful in acting as anti-ballistic armor or in other applications which may require a steel sheet having high hardness in combination with high ductility.
Disclosed is a method for treating a steel article to form a high yield strength and ductile alloy comprising the steps of:
(a) providing a steel composition having a material thickness no greater than 0.5 inches (12.7 mm), having an initial microstructure of at least ferrite and pearlite, and having a composition of, by weight,
carbon between 0.25 and 0.55%,
silicon between 0.15 and 0.35%,
manganese between 0.40 and 1.0%,
chromium between 0.40 and 1.10%,
nickel less than 4.5%,
molybdenum between 0.15 and 0.35%,
sulfur less than 0.040%,
phosphorus less than 0.035%, and
balance iron and other elements and compounds in making steel;
(b) preheating the provided steel composition to not more than 594° C. (1100° F.);
(c) heating the provided steel composition to a peak temperature of between 800° C. (1472° F.) and 1150° C. (2102° F.) in less than forty seconds;
(d) holding the heated steel composition at the peak temperature range for between two and twenty seconds;
(e) quenching the heated steel composition from the peak temperature range to below 117° C. (350° F.) at a temperature rate reduction of between 200 and 3000° C./sec (360-5400° F./sec);
(f) removing residual quench media from the surface of the quenched steel composition;
(g) tempering the quenched steel composition at a temperature from 100° C. to 704° C. (212-1300° F.) for less than ninety minutes;
(h) air cooling the tempered steel composition to less than 100° C. (212° F.) to form a steel article having at least 80% martensite and up to 5% bainite by weight, a yield strength of at least 160 Ksi (1100 MPa), and a total elongation between 5% and 22%.
Additionally, the air cooled steel composition may have a V50 protection ballistic limit at 30° obliquity angle at least 2300 feet per second (701 m/s) with a .30 caliber armor piercing round for a thickness of 0.25 inches (6.35 mm).
The air cooled steel composition may have a microstructure with no more than 1% bainite, by weight.
Alternatively, disclosed is a method for treating a steel article to form a high yield strength and ductile alloy comprising the steps of:
(a) providing a steel composition having a material thickness no greater than 0.5 inches (12.7 mm), having an initial microstructure of at least ferrite and pearlite, and having a composition of, by weight,
carbon between 0.25 and 0.55%,
silicon between 0.15 and 0.35%,
manganese between 0.40 and 1.0%,
chromium between 0.40 and 1.10%,
nickel less than 4.5%,
molybdenum between 0.15 and 0.35%,
sulfur less than 0.040%,
phosphorus less than 0.035%, and
balance iron and other elements and compounds in making steel;
(b) preheating the provided steel composition to not more than 594° C. (1100° F.);
(c) heating the preheated steel composition to a peak temperature of between 800° C. (1472° F.) and 1150° C. (2102° F.) in less than forty seconds;
(d) holding the heated steel composition at the peak temperature range for between two and twenty seconds;
(e) quenching the heated steel composition from the peak temperature range to below 177° C. (350° F.) at a temperature rate reduction of between 200 and 3000° C./sec (360-5400° F./sec);
(f) removing residual quench media from the surface of the quenched steel composition; and
(g) air cooling the steel composition to less than 100° C. (212° F.) to form a steel article having at least 80% martensite and up to 5% bainite by weight, a yield strength of at least 160 Ksi (1100 MPa), and a total elongation between 5% and 22%.
Additionally, the air cooled steel composition may have a V50 protection ballistic limit at 30° obliquity angle at least 2300 feet per second (701 m/s) with a .30 caliber armor piercing round for a thickness of 0.25 inches (6.35 mm).
Also disclosed is a method for treating a steel article to form a high yield strength and ductile alloy comprising the steps of:
(a) providing a steel composition having a material thickness no greater than 0.5 inches (12.7 mm), having an initial microstructure of at least ferrite and pearlite, and having a composition of, by weight,
carbon between 0.25 and 0.55%,
silicon between 0.15 and 0.35%,
manganese between 0.40 and 1.0%,
chromium between 0.40 and 1.10%,
nickel less than 4.5%,
molybdenum between 0.15 and 0.35%,
sulfur less than 0.040%,
phosphorus less than 0.035%, and
balance iron and other elements and compounds in making steel;
(b) preheating the provided steel composition to not more than 815° C. (1500° F.);
(c) heating the preheated steel composition to a peak temperature of between 800-1150° C. (1472-2102° F.) in less than forty seconds;
(d) holding the heated steel composition at the peak temperature range for between two and twenty seconds;
(e) quenching the heated steel composition to below 177° C. (350° F.) in less than four seconds;
(f) removing residual quench media from the surface of the quenched steel composition;
(g) tempering the quenched steel composition at a temperature between 100° C. and 704° C. (212-1300° F.) for less than ninety minutes; and
(h) air cooling the tempered steel composition to less than 100° C. (212° F.) having a transformed microstructure of at least 80% martensite and up to 5% bainite by weight, a yield strength of at least 160 Ksi (1100 MPa), and a total elongation between 5% and 22%.
Additionally, the air cooled steel composition may have a microstructure with no more than 1% bainite by weight.
Alternatively, disclosed is a method for treating a steel article to form a high yield strength and ductile alloy comprising the steps of:
(a) providing a steel composition having a material thickness no greater than 0.5 inches (12.7 mm), having an initial microstructure of at least ferrite and pearlite, and having a composition of, by weight,
carbon between 0.25 and 0.55%,
silicon between 0.15 and 0.35%,
manganese between 0.40 and 1.0%,
chromium between 0.40 and 1.10%,
nickel less than 4.5%,
molybdenum between 0.15 and 0.35%,
sulfur less than 0.040%,
phosphorus less than 0.035%,
balance iron and other elements and compounds in making steel;
(b) preheating the provided steel composition to a temperature to not more than 815° C. (1500° F.);
(c) heating the preheated steel composition to a peak temperature between 800° C. (1472° F.) and 1150° C. (2102° F.) in less than forty seconds;
(d) holding the heated steel composition at the peak temperature range for between two and sixty seconds;
(e) quenching the heated steel composition from the peak temperature range to below 100° C. (212° F.) at a temperature rate reduction of between 200 and 3000° C./sec (360-5400° F./sec);
(f) removing residual quench media from the surface of the quenched steel composition;
(g) tempering the quenched steel composition at a temperature from 100° C. to 704° C. (212-1300° F.) for less than ninety minutes; and
(h) air cooling the tempered steel composition to less than 100° C. (212° F.) to form a steel article having at least 80% martensite and up to 5% bainite by weight, a yield strength of at least 160 Ksi (1100 MPa), and a total elongation between 5% and 22%.
Alternatively, the air cooled steel composition has a V50 protection ballistic limit at 30° obliquity angle of at least 2300 feet per second (701 m/s) with a .30 caliber armor piercing round for a thickness of 0.25 inches (6.35 mm).
Additionally, the air cooled steel composition may have a microstructure with no more than 1% bainite by weight.
Alternatively, disclosed is a method for treating a steel article to form a high yield strength and ductile alloy comprising the steps of:
(a) providing a steel composition having a material thickness no greater than 0.5 inches (12.7 mm), having an initial microstructure of at least ferrite and pearlite, and having a composition of, by weight,
carbon between 0.25 and 0.55%,
silicon between 0.15 and 0.35%,
manganese between 0.40 and 1.0%,
chromium between 0.40 and 1.10%,
nickel less than 4.5%,
molybdenum between 0.15 and 0.35%,
sulfur less than 0.040%,
phosphorus less than 0.035%,
balance iron and other elements and compounds in making steel;
(b) preheating the provided steel composition to not more than 594° C. (1100° F.);
(c) heating the preheated steel composition to a peak temperature of between 800-1150° C. (1472-2102° F.) in less than forty seconds;
(d) holding the heated steel composition at the peak temperature range for between two and sixty seconds;
(e) quenching the heated steel composition from the peak temperature range to below 177° C. (350° F.) in less than four seconds;
(f) removing residual quench media from the surface of the quenched steel composition;
(g) tempering the quenched steel composition at a temperature from 100° C. and 704° C. (212-1300° F.) for less than ninety minutes; and
(h) air cooling the tempered steel composition to less than 100° C. (212° F.) having a transformed microstructure of at least 80% martensite and up to 5% bainite by weight, a yield strength of at least 160 Ksi (1100 MPa), and a total elongation between 5% and 22%.
The air cooled steel composition may have a microstructure with no more than 1% bainite by weight.
Additionally, the air cooled steel composition may have a V50 protection ballistic limit at 30° obliquity angle at least 2300 feet per second (701 m/s) with a .30 caliber armor piercing round for a thickness of 0.25 inches (6.35 mm).
The steel composition may be heated in step (c) in less than twenty seconds. Further, the heated steel composition may be held at the peak temperature range for between two and twenty seconds. Further, the heated steel composition may be quenched from the peak temperature range to below 177° C. (350° F.) at a temperature rate reduction of between 200 and 3000° C./sec (360-5400° F./sec). Further, the residual quench media may be removed from the surface of the quenched steel composition by at least one of mechanical wiping, blown air, and combinations thereof. Alternatively, the tempering step is performed using a conventional oven. The tempering step may be performed using a combination of conventional oven and induction heater Additionally, the tempering step may be performed at between 100° C. (212° F.) and 704° C. (1300° F.).
Alternatively disclosed is a method for treating a steel article to form a high yield strength and ductile alloy comprising the steps of:
(a) providing a steel composition having a material thickness no greater than 0.5 inch (12.7 mm), having an initial microstructure of at least ferrite and pearlite, and having a composition of, by weight,
carbon between 0.25 and 0.55%,
silicon between 0.15 and 0.35%,
manganese between 0.40 and 1.0%,
chromium between 0.40 and 1.10%,
nickel less than 4.5%,
molybdenum between 0.15 and 0.35%,
sulfur less than 0.040%,
phosphorus less than 0.035%,
balance iron and other elements and compounds in making steel;
(b) preheating the provided steel composition to not more than 594° C. (1100° F.);
(c) heating the preheated steel composition to a peak temperature between 800-1150° C. (1472-2102° F.) in less than forty seconds;
(d) holding the heated steel composition at the peak temperature range for between two and sixty seconds;
(e) quenching the heated steel composition to below 177° C. (350° F.) in less than four seconds;
(f) removing residual quench media from the surface of the quenched steel composition; and
(h) air cooling the steel composition to less than 100° C. (212° F.) having a transformed microstructure of at least 80% martensite and up to 5% bainite by weight, a yield strength of at least 160 Ksi (1100 MPa), and a total elongation between 5% and 22%.
In any of the embodiments, prior to heating the steel composition, two or more lengths of steel plates may be welded together along the width with one or more welds to form a continuous series of steel plates. Further, the step of welding may include applying a weave weld bridging between lengths of steel plate across the width of the steel plates. Further, the step of welding may include applying a weave weld bridging between lengths of steel plate in three sections where the center portion of steel plate is done first and the side portions are welded to provide a weave weld across the width of the steel plates. In any event, a seam weld is applied over the weave weld across the width of the steel plates. Further, an indicia may be applied to the steel plate in advance of the welding step to enable a vision system to identify the location of end portions of lengths of the steel plates for the welding step.
The heating step may be performed using an induction heater. The quenching step may be performed by flowing a quench medium over the steel article at a rate of up to 900 gallons/min (3400 L/min). The quench medium may be water. The quenching step may be performed in more than 1 second and not more than 20 seconds. After the quenching step, the steel plate is cut into lengths at least at the seams while the steel plate continuously moves along the conveyor.
The tempering step may also be performed using an induction heater. The tempering step may be performed at between 100° C. (212° F.) and 704° C. (1300° F.) in a time between 1 and 20 seconds.
Additionally, the steel composition may have, by weight, carbon between 0.25 and 0.40%. Alternatively, the carbon composition may be between 0.40 and 0.55%.
Additionally, the air cooled steel composition may have a microstructure having no more than 1% bainite by weight.